Conventionally, sensors for measuring a blood component have been used for clinical tests, self-measurement of blood glucose level by diabetics, etc. The configuration of the sensor for measuring a blood component is such that, for example, a cover is disposed on an insulating substrate having a working electrode and a counter electrode on its surface with a spacer intervening between the cover and the insulating substrate. On the working electrode and the counter electrode, a reagent containing an oxidoreductase, a mediator (an electron carrier), and the like is provided, thereby forming an analysis portion. The analysis portion communicates with one end of a channel for leading blood to the analysis portion. The other end of the channel is open toward the outside of the sensor so as to serve as a blood supply port. Blood component analysis (e.g., analysis of blood glucose level) using the sensor configured as above is carried out in the following manner, for example. First, the sensor is set in a dedicated measuring device (a meter). Then, a fingertip or the like is punctured with a lancet to cause bleeding, and the blood supply port of the sensor is brought into contact with the blood that has come out. The blood is drawn into the channel of the sensor by capillary action and flows through the channel to be led to the analysis portion where the blood comes into contact with the reagent. Then, a redox reaction occurs between a component in the blood and the oxidoreductase so that a current flows via the mediator. The current is detected, and the measuring device calculates an amount of the blood component based on the detected current and displays the value obtained by the calculation.
In the above-described manner, the sensor can measure the blood component. However, since the obtained measured value might be affected by a hematocrit (Hct), it might be necessary to measure a Hct value and then correct the amount of the blood component based on this Hct value in order to obtain an accurate measured value. For example, there has been a sensor that corrects an amount of a blood component by measuring a Hct value by the use of two working electrodes and one reference electrode (see Patent Document 1). Other than this, there has been a method in which a Hct value is measured using a mediator (see Patent Document 2). However, the conventional technique has a problem concerning the accuracy and the reliability of the measured Hct value so that the amount of the blood component cannot be corrected sufficiently and accurately.    Patent Document 1: JP 2003-501627 A    Patent Document 2: Japanese Patent No. 3369183